Process for production of synthetic leather

ABSTRACT

A synthetic leather is produced by impregnating a fiber web with a binder solution, coating one surface of the said web with a solution of a synthetic resin having a viscosity higher than that of the said binder solution before the said binder is coagulated, and thereafter coagulating the said binder and the synthetic resin simultaneously. In another embodiment, it is produced by impregnating a fiber web with a binder solution, applying to one surface of the said web at least one kind of binder solution having a viscosity higher than that of the first-mentioned binder solution in the order of a lower viscosity before the already applied binders are coagulated, applying to the said surface a solution of a synthetic resin having a viscosity of 50-10,000 poises, and thereafter coagulating the said binders and the synthetic resin simultaneously.

United States Patent Inventors Appl. No. Filed Patented AssigneesPriority PROCESS FOR PRODUCTION OF SYNTHETIC LEATHER 6 Claims, 3 DrawingFigs.

US. Cl 156/148, 156/306, 156/315 Int. Cl B32b 23/02 Field of Search 156/148 [56} References Cited UNITED STATES PATENTS 1,825,827 10/1931 Smith156/148 X 3,197,355 7/1965 Copeland 156/148 X 3,321,356 5/1967 Merrimonet a1 156/148 X Primary ExaminerCarl D. Quarforth AssistantExaminer-Gary G. Solyst AttarneyWenderoth, Lind & Ponaek ABSTRACT: Asynthetic leather is produced by impregnating a fiber web with a bindersolution, coating one surface of the said web with a solution of asynthetic resin having a viscosity higher than that of the said bindersolution before the said binder is coagulated, and thereaftercoagulating the said binder and the synthetic resin simultaneously. Inanother embodiment, it is produced by impregnating a fiber web with abinder solution, applying to one surface of the said web at least onekind of binder solution having a viscosity higher than that of thefirst-mentioned binder solution in the order of a lower viscosity beforethe already applied binders are coagulated, applying to the said surfacea solution of a synthetic resin having a viscosity of 5010,000 poises,and thereafter coagulating the said binders and the synthetic resinsimultaneously.

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o O O PATENTED SEP21 1971 APPARENT DENSITY (9/cm APPARENT DENSITY (9/Cmlb THICKNESS (mm) THICKNESS (mm) T 0; HI K A7. sumo HAM 11v vlszv'mmHmosm Hm'fon Ana KBNOSUKE mmwmwm BY Mud/" 4 M This invention relates toa process for the production of a synthetic leather comprising a fiberweb as a substrate and a synthetic resin as a surface layer. Moreparticularly, the invention relates to a process for theproduction of asynthetic leather by impregnating a fiber web with a binder solution,coating the web with a solution of a synthetic resin having a viscosityhigher than that of the said binder solution before the binder iscoagulated, and thereafter coagulating the said binder and syntheticresin simultaneously.

Methods of producing a synthetic leather having a surface layer of asynthetic resin are already known and some examples are as follows:

l. A method by which the surface of a woven or knitted article is coatedwith a synthetic resin;

2. A method by which the surface of a nonwoven fabric is coated with asynthetic resin; and,

3. A method by which a nonwoven fabric is caused to adhere to the undersurface of a woven article coated with a synthetic resin.

None of these methods, however, give an interior structure having acontinuous density gradient like that of a natural leather, and theresulting product disadvantageously does not look like leather inrespect of its behavior towards fiexural deformation or ability offorming a bended surface. Synthetic leathers obtained by methods 1 and 3are not characterized by the absence of orientation as seen in a naturalleather because the orientation of the woven article as substrateappears in them as their own orientation, and therefore they arerestricted in their use as leather. Furthermore, the synthetic leatherobtained by method (1) encounters a great difficulty when processed atits back surface, for instance, in a shoemaking process, especially aside-buffing operation because its properties relating to strengthmostly depend on the woven article. According to method 2, a syntheticresin is coated on a dried nonwoven fabric as a surface layer. It isimpossible therefore for this method to obtain an integrated areaconsisting of the resinous surface layer and the binder, and to give asynthetic leather satisfactory in respect of density gradient andcohesion between layers.

Some of the known methods of giving a density gradient to a nonwovenfabric are as follows; that is, a method by which a binder is applied toa laminate consisting of a plurality of fiber webs each having adifferent denier or the laminate is punched; a method by which alaminate consisting of a plurality of fiber webs each having a differentshrinkage is punched, and then subjected to a shrinkage treatment; amethod by which the depth of a needle penetration into the laminate iscontrolled; and a method of imparting a density gradient by applying abinder or paste to a nonwoven fabric, and pressing it thereinto from theside on which it is applied or sucking it from the opposite side. Butall of these methods are complicated in respect of operation andapparatus. In addition, all of the products obtained necessitate thecoating of a resin on a nonwoven fabric to obtain a leatherlike glossysurface, and also it is difficult in such products to integrate thesurface resinous layer and the nonwoven fabric layer, which results in atendency of the layers to separate from each other.

An object of this invention is to remove the abovementioned defects, andto provide a synthetic leather having a structure and an outerappearance like those of a natural leather in which an interface of abinder for a nonwoven fabric and that of a resin in a surface layer areintegrated whereby a high strength is retained against the separation ofthe surface resinous layer from the nonwoven fabric.

Another object of this invention is to provide a synthetic leatherhaving an interior structure with a density gradient.

Other objects of the invention will become apparent from the descriptionwhich follows.

A synthetic leather which conforms to these objects of the invention canbe obtained by impregnating a fiber web with a binder solution, coatingone surface of the said web with a solution of a synthetic resin havinga viscosity higher than that of the said binder solution before thebinder is coagulated, and thereafter simultaneously coagulating thebinder impregnated among the fibers of the web and the resin coated onthe surface of the web thereby to integrate them.

In the accompanying drawings:

FIG. 1 is a cross-sectional view of the synthetic leather according tothis invention; and

FIGS. 2 and 3 are graphs showing a density gradient.

As the fiber to constitute the fiber web of this invention, a naturalfiber such as cotton, flax, silk and wool, a regenerated fiber such asrayon, and a synthetic fiber such as polyamide, polyester,polyacrylonitrile and polyolefine are used either singly or incombination. These fibers may be modified by an ordinarily known methodsuch as composite-spinning, copolymerization and grafting. And thesefibers may have a denier of 0.5 to l0,but from the standpoint of tactilehand as synthetic leather, the denier of 1.5 to 4 is most preferable.The fiber length is preferably in the range of 10 mm. to mm., especiallypreferred being a length of 38 mm. to 76 mm. in view of the tactile handand operability as synthetic leather.

The fiber web as a substrate of the synthetic leather of this inventionis prepared from such fiber by a customary method and apparatus such ascard, gamett and random webber. A preferable fiber web has a weight perunit area of l00-l ,000 g./m. especially 200-300 g./m. lf necessary, theintertwining of the individual fibers with each other can be enhanced byneedle-punching such web. The conditions for punching may be determineddepending on the denier of the fiber to be used, the fiber length, thetype of the fiber to be used, the weight of the web per unit area andthe properties required of a final product. Under the ordinarily usedconditions, punching is carried out by using needles (No. 32-42,Standard of The Torrington Co., U.S.A.) with the number of penetrationof 200 800, particularly 300-500, per square centimeter and a needlepenetration depth of 6-12 mm. The web can also be set by compressionwith a hot roll instead of punching.

The binder to be impregnated into the fiber web and the synthetic resinto be applied on its surface preferably have a chemical composition ofthe same series as they are coagulated simultaneously. Preferable resinsto be used as the binder and the surface layer-forming synthetic resinare thermoplastic resins such as polyamides, polyesters, poly(vinylchloride), polyacrylonitrile and polyurethane. They may be used incombinations of two or more. These resins are applied to the fiber webin the form of a solution in a solvent which is nonsolvent for thefibers that make up the fiber web. The solution of the synthetic resinfor forming a surface layer should have a viscosity higher than thebinder solution does. The viscosity of the solution of the surface layerresin is in the range of 20 to 10,000 poises, and that of the bindersolution is chosen within the range of 0.] to 100 poises. If desired, afiller I such as wood powder and calcium carbonate, a pigment such ascarbon black, an antifoaming agent. or an antioxidant can beincorporated into a solution of the synthetic resin.

ln impregnating the fiber web with the binder solution, it is preferableto press the binder uniformly into the interior layer of the web byusing a squeezing device such as screen and mangle. Subsequent to thisoperation, the synthetic resin for the surface layer is coated all overone surface of the web by means of a reverse roll coater or knife coaterbefore the binder is coagulated. in this manner, the surfacelayer-forming resin is applied before the binder is coagulated and aliquidliquid mixing is effected at the interfaces. Consequently, whenthe surface layer of the synthetic resin and the binder aresimultaneously coagulated, the web an surface layer are integrated to anextent such that they may not be separated from each other.

The coagulation of the binder and the surface layer-forming resin iscarried out by two ways, one of which is a wet method wherein thesolvent is extracted in a liquid such as water which is compatible withthe solvent, and the other of which is a dry method wherein the solventextraction: is carried out by such operation as heating. Inconsideration of the state of the resin after Coagulation and the shapeof the cell, the wet method is desirable to get a synthetic leather. Asa porous structure is formed on the surface layer by solvent extractionin a coagulating step, the intended synthetic leather akin to a naturalleather can be obtained by water-washing and drying after thecoagulating step. To enhance the smoothness of the surface layer, theresulting leather is pressed while heating at a temperature below themelting point of the fiber of the web and above the softening point ofthe resin.

The synthetic leather obtained in this manner may be subjected to anembossing apparatus. For the purpose of enhancing the gloss and hue ofthe surface, a paint such as nitrocellulose lacquer may be applied tothe leather by spraying, coating or printing.

According to a modification of the process described above, the densitygradient of the structure can be made more resembling to that of anatural leather by changing the method of applying a binder solution toa fiber web. Namely, according to a specific embodiment of thisinvention, a synthetic leather having such density gradient can beobtained by impregnating a fiber web with a binder solution, applying atleast one kind of binder solution having a viscosity higher than that ofthe firstmentioned binder solution to one surface of the said web in theorder of a lower viscosity before the already applied binders arecoagulated, coating the said surface with a solution of a syntheticresin having a viscosity preferably higher than that of the last-appliedbinder solution before these binders are coagulated, and thereaftercoagulating the said binders and the synthetic resin simultaneously.Thus, a density gradient changing continuously from the surface layer tothe back layer is formed. The binder is present in the web inconcentration higher towards the surface owing to the difference in theamount of the binder to be penetrated into the web which is caused bythe difference in viscosity of the binder solutions applied in sequence.

Hence, the structure of the synthetic leather obtained according to thisembodiment of the invention is not a simple laminated structure as seenin the conventional synthetic leather, but looks almost like that of anatural leather. The behavior of this synthetic leather towards bendingdeformation is almost the same as that of a natural leather, too.

Of course, the same kind of a substrate web, binder and synthetic resinof the surface layer can be used in this embodiment, and the same methodis also used in coagulation.

Since in this embodiment, the difference in viscosity of the bindersolutions gives a density gradient changing continuously from thesurface layer to the back layer of the web, the density gradient is moregentle as more kinds of binder solution of different viscosity are used,with the result that the structure is more like that of a naturalleather. It is however desirable to restrict the number of binderapplying procedures to two to three times because of disadvantages inproductivity and cost of production.

In fact, a synthetic leather satisfactory for practical purposes can beobtained by impregnating a web with a binder solution, applying a bindersolution having a viscosity higher than that of the first-mentionedbinder solution to one surface of the web, further coating the saidsurface with a solution of a synthetic resin for a surface layer havinga viscosity preferably higher than that of the said binder solution, andthereafter coagulating the said binders and the synthetic resin. ln thismethod, the binder solution to be impregnated into the web has aviscosity of 01-100 poises, and the second-applied binder solution andthe finally coated synthetic resin solution both have a viscosity in therange of 50 to 10,000 poises.

The, binder first impregnated into the web is primarily intended to bondindividual fibers of the web at intersecting points, and thenext-applied binder is intended to bring about a density gradient byutilizing its smaller amount of penetration (distance of penetrationfrom the surface on which the binder is applied) than the first-appliedbinder which is penetrated throughout the section of the web, and alsoto set the individual fibers of the web at the surface layer. The

synthetic resin finally coated on the web surface is for the purpose ofenhancing the outer appearance of the product as a leather, and toimprove such mechanical properties as resistance to scuffing and toflexural fatigue.

FIG. 1 of the accompanying drawings is an enlarged sectional view of thesynthetic leather obtained bythe abovementioned embodiment of thisinvention. The reference numeral 1 represents a microcell structure, 2 amacrocell structure, 3 and 4, a nylon 6 fiber that makes up the web, 5,a binder impregnated into the web at the outset and a filler, 6, amicroporous film composed of a filler and a synthetic resin for forminga surface layer which is coated in the last place, and 7, a structurehaving a density gradient formed of the first-impregnated bindersolution and the next-applied binder solution having a higher viscosity.in the synthetic leather of this invention obtained in theabove-mentioned manner, the binders in the web and the surfacelayer-forming resin are simultaneously coagulated and integrated attheir interface, and so it has a high cohesion between layers. Also,because of the penetration of the surface resin into the interior of theweb, a density gradient is provided from the surface to the back surfaceby the surface layer resin and the binders. It is therefore possible forthe method of this invention to provide a structure having a densitygradient continuous from the flesh side to the grain surface side and astructure wherein the flesh side and the grain side are integrated.Furthermore, because of a complete setting by the resin of individualfibers near the surface layer, the traces of punching do not appear onthe surface of the synthetic leather of this invention in a processingprocedure in which the leather is processed in an elongated state, forinstance in toe-lasting step of shoemaking. In other words, the surfaceof the synthetic leather is not roughened.

Now, the invention will be described by way of working examples.

EXAMPLE 1 A web having a weight per unit area of 300 g./m. was producedby means of a random webber from nylon 6 staples having a denier of 4, afiber length of 51 mm., a titanium oxide content of 0.2 percent, and anumber of crimps of i5 turns/25 This web was needle punched by means ofa needle-loom (James Hunter Co., U.S.A.). The needles used were regularbarbs (standard No. 42 of The Torrington Co., U.S.A.). The number ofneedle penetration per square centimeter was 500, and the needlepenetration depth was 8 mm. The resulting punched web was immersed in a15 percent solution (with a viscosity of 20 poises) in dimethylformamideof a polyester polyurethane prepared by chain-extending with butanediola prepolymer form polyethylene adipate having a molecular weight ofabout 2,000 and diphenylmethane-4,4'-diisocyanate (MDl), compresseduntil the takeup reached 20 parts by weight as against l00 parts of thefiber, and then immediately coated on its one surface with a 20 percentsolution (with a viscosity of 128 poises) in dimethylformamide of thesame polyester polyurethane as mentioned above by using a blade with aclearance of 2.0 mm. The so treated web was deprived of the solvent bypouring it into water (coagulation bath) at 20 C. The time needed forthe solvent extraction was 20 minutes. After complete coagulation, itwas washed with water, and dried. There was obtained a synthetic leatherhaving a total thickness of 1.5 mm. which is composed of an about l.1mm. thick interior structure having a continuous density gradientprovided by the binders and the resin on the surface layer and an about0.4 mm. thick porous film of the resin of the surface layer. The densitygradient of this synthetic leather is shown in FIG. 2.

The same punched web was impregnated with the same 15 percent bindersolution in the same amount, and after coagulating, water washing anddrying the so impregnated binder solution, the said 20 percent resinsolution was applied to one surface of the web and then coagulated. Theresulting synthetic leather was designated as control synthetic leather(corresponding to the conventional article obtained by method 2mentioned at the outset of this specification). A comparison of thiscontrol leather with the synthetic leather obtained by this examplereveals, as shown in table 1, that the synthetic leather according tothe method of this invention is remarkably superior to the controlproduct in respect of pliability and water permeability, and noseparation between the surface resin layer and the nonwoven fabric isseen.

with dimethylformamide to make a solution having a viscosity of 20poises. In this solution the same punched web as used in example i wasimmersed, and squeezed until the takeup of the solid content reached 60parts as against 100 parts of the fiber of the web. Immediatelythereafter, a resin solution for forming a surface layer was applied toone surface of the so treated web by means of a knife coater. This resinsolution had been prepared by adding 5 parts, based on. l parts of thesolid polyurethane, of carbon black to the said polyurethane solu- TABLE1 Cohesion Apparent Tensile Elongation Gureys Water perbetween Thicknessdensity strength at break stiffness meability layers (mm.) (g./em.(kg/cm.) (percent) (mg) (g./m. hr.) (kg./2 cm.)

Synthetic leather of this invention 1. 50 0.56 18.0 120 2, 350 1, 750Inseparable Control synthetic leather 1. 50 0.55 15. 1 90 3, 500 1, 0032.0

EXAMPLE2 tion having a concentration of 35 percent and a viscosity ofOne mole of poly (e-caprolactone) having a molecular weight of 1850 andan acid value of 0.1 l was reacted with 2 moles ofdiphenylmethane-4,4'-diisocyanate to form a prepolymer having amolecular weight of 2530. One mole of the resulting prepolymer and 0.985mole of ethylene diamine are chain-extended in dimethylformamide to givea 25 percent polyurethane solution having a viscosity of l,250 poises.This solution was diluted to l5 percent with dimethylformamide to make asolution having a viscosity of 13 poises. [n this solution, the samepunches web as used in example 1 was immersed, and squeezed by a mangleuntil the takeup of the solid polyurethane content reached 50 parts asagainst 100 parts of the fiber of the web. A resin solution having aviscosity of 2,000 poises and a solid content concentration of 30percent was applied to one surface of the web by means of a reverse rollcoater. This resin solution had been prepared by incorporating into thepolyurethane solution 35 parts of poly (vinyl chloride) and 20 parts ofa plasticizer (DOP), all amounts being based on 100 parts of the solidpolyurethane, and adjusting its concentration to 30 percent with the useof dimethylformamide.

The coagulating, water-washing, and drying treatments of the so treatedweb under the same conditions as in example 1 gave a synthetic leatherhaving a good tactile hand.

EXAMPLE 3 A polyurethane prepolymer was prepared by reacting 2 moles ofpolytetrahydrofuran having a molecular weight of 2,080 with 3.2 moles ofa mixture of 2,4-tolylenediisocyanate with 2,6-tolylenediisocyanate.This prepolymer was reacted with an equimolar amount of hydraxinehydrate in dimethylformamide to form a polyurethane solution. Acopolymer of 65 mole butadiene and 35 mole acrylonitrile in an amountsame as that of the polyurethane solid content was dissolved into theresulting polyurethane solution, and diluted with dimethylformamide togive a solution having a viscosity of 5 poises and a solid concentrationof percent.

With the use of the resulting solution as a binder solution, the sameprocedure as that of example 2 was followed except that a knife coaterwas used instead of the reverse roll coater. The obtained product wasserviceable as a synthetic leather as it had a strong cohesion betweenlayers and a density gradient owing to the penetration of the surfacelayer resin solution into the interior of the web.

EXAMPLE 4 A prepolymer was prepared by reacting poly (1,4-butyleneadipate) having a molecular weight of 2,000 and an acid value of 4.6with diphenylmethane-4,4'-diis0cyanate. The resulting prepolymer wasreacted with butanediol in dimethylformamide to effect chain extensionto form a polyurethane solution having a viscosity of 520 poises and aconcentration of 35 percent. This polyurethane solution was diluted topercent 520 poises, and adjusting the concentration and the viscosity to36.7 percent and 560 poises respectively.

The same coagulating, water'washing and drying treatments as those of lI gave a synthetic leather having a good tactile hand.

EXAMPLE 5 A web having a weight per unit area of 200 g./m. was producedfrom nylon 6 staples having a denier of 1.5, a fiber length of 38 mm., anumber of crimps of 15 turns/inch, and a titanium oxide content of 0.2percent by means of a random webber. The web was passed through a pairof hot rolls heated to 160 C., compressed and set. The same treatment asthat of example I gave a synthetic leather having a good tactile hand.

EXAMPLE 6 A web having a weight per unit area of 250 g./m.. was producedfrom a polyester fiber having a denier of 1.5, a fiber length of 38 mm.,and a number of crimps of i5 turns/inch by means of a cross lappcr. Theweb was punched by a needle loom (James-Hunter C0,, U.S.A.) with thenumber of needle penetration of LOGO/cm, and the needle penetrationdepth of 6 mm. The so treated web was passed through a pair of hot rollsheated to 160 C., and the thickness after hot-pressing was adjusted to1.0 mm.

A copolymer of 65 mole butadiene and 35 mole acrylonitrile was dissolvedin dimethylformamide to a concentration of l5 percent to make a solutionhaving a viscosity of6 poises. The web was immersed in this solution,and squeezed by a mangle until the takeup of the solid copolymer contentreached 50 parts as against parts of the fiber of the web. Immediatelythereafter, a resin solution for forming a surface layer was applied toone surface of the web by means of a reverse roll coater. This resinsolution had been prepared by adding to the said copolymer solution 20parts of cellulose powder having an average particle size of 20 micronsand 5 parts of carbon black, all amounts being based on 100 parts of thecopolymer and adjusting the concentration and the viscosity of thesolution to 30 percent and 230 poises respectively with the useofdimethylformamide.

The same coagulating, water-washing and drying treatments of the webgave a synthetic leather conforming to the objects of this invention.

EXAMPLE 7 One hundred parts of a copolymer composed of 35 moles of vinylacetate and 65 moles of vinyl chloride, 20 parts of carbon black, 50parts of a plasticizer (DOP) and 35 parts of calcium carbonate weredissolved in dimethylformamide to make a solution having a concentrationof 30 percent and a viscosity of 100 poises. With the use of theresulting solution as a resin solution for forming a surface layer, thesame procedure as that of example 6 was followed, and a syntheticleather conforming to the objects of this invention was obtained.

EXAMPLE 8 parts by weight of the fiber of the web. immediatelythereafter, without coagulating the solution, solution III was appliedto the same surface by means of a knife coater until the takeup of thesolid content reached 48 parts by weight as against 100 parts by weightof the fiber of the web. The so treated web was immersed in water at 20C. for 15 minutes to coagulate the solution, immersed in an open soapingat 80 C. for 20 minutes, washed with water, and dried.

Sample B was obtained by impregnating the needlepunched web with thesaid solution I, coagulating it, applying solution I] to one surface ofit, coagulating it in water in the like manner, and drying it.

Commercially available sample A is a synthetic leather wherein a wovenfabric is disposed between the substrate and the surface coat, andcommercially available sample B is a synthetic leather wherein a wovenfabric is not disposed between them.

A web having a weight per unit area of 250 g./m. was produced from nylon6 staples having a denier of 3.5, a fiber length of 51 mm., a titaniumoxide content of 0.2 percent and a number of crimps of i5 turns/25 mm.by means of a random webber. The web was punched by means of a needleloom (James-Hunter Co., U.S.A.). The used needles were standard No. 42regular barbs of The Torrington Co., U.S.A. The number of needlepenetration was 500/cm, and the needle 10 penetration depth was 10 mm.

A prepolymer was prepared from polyethylene adipate having a molecularweight of about 2,000 and MD], and chain extended with butanediol toform polyester polyurethane. A mixture composed of 80 parts of thispolyurethane, 20 parts of carbon black and 60 parts of pulp wasdissolved into dimethylformamide to form three solutions having a solidcontent concentration of 15 percent (solution I), 30 percent (solutionii),

and 4 0 percent (solution lll), respectively. The viscosity of theEXAMPLE 9 solution was 19 poises (for solution I), l00 poises (forsolution 20 ll), and 1,000 poises (for solution lll). As mentionedherein- A pr p y having a molecular Weight of 2,530 was below, thesesolutions were applied to the said web in the P p y reacting 1 mole f ply(c-caprolaC havinga order of alower viscosity. molecular weight of1,850 and an acid value of 0.11 with 2 The web was dip coated with ol tiil h takeup f moles of diphenylmethane-4,4'-diisocyanate. One mole ofthis the solid content reached 40 parts by weight as against 100 p lf ywas "f' with 0985 mole of ethylencdiamlne parts by weight of the web.Immediately thereafter, without in y Sulfoxldc to form a 25 PercentPolyurelhane Solu' any solvent extraction procedure, solution II wasapplied to f 3 9 of L p From Solution, the same surface to which thesolution I had been applied by three e of reel" eelutlens were p p e theSame means of a reverse roll coater until the takeup of the solidconmanner as example 3, that Is, a Solutlo" havmg a concentratentreached 54 parts by weight as against 100 parts by weight tion of pefcemand a Viscosity p i Q Solution having f the Finallyy Solution m wasapplied to the Same a concentration of 18 percent and a viscosity of 80poises face until the takeup of the solid content reached 48 parts by Pp e y ing 5 parts, based on 100 parts by weight of weight as against 100parts by weight of the fiben the solld polyurethane, of carbon black tothe original solu- The so named web was then conducted to a water vesselat tion, and diluting it with dimethyl sulfoxide to a concentration 20C., and immersed in it for 18 minutes to effect solvent exof percent anda re.sm Sohmon having a vlscofliy of 270 traction and coagulation of theresin. To remove the solvent p' P F 9 carbon black to the orlgmalcompletely the web was immersed far 20 minutes in an Open tron anddiluting it with dimethyl sulfoxide to a concentration soaper at 80 C.after coagulation of the resin washed with of 20 percent synthetlc lwere. producgd water and dried The obtained Synthetic leather was g inthese three kinds of solution having a different viscosity and tactilehand, and consisted of about 1.1 mm. of a thick sub- 40 lmpreg-natmgcoatmg coagulatmg watqr washmgl ER strate layer and about 0.4 mm. of athick surface layer with a according to the Same procedures as m examp eese synthetic leathers had a continuous density gradient and a zazrgentle density gradlent caused by the rcsm and the strong cohesionbetween layers. Excellent shoes could be made from h s th t'c leatherswithout surface rou hen- Now, the synthetic leather of this inventionw|ll be comt 656 yn e I g pared with the synthetic leathers obtained bythe conventional mg m the meilastmg of a Shoe-making processmethod andthe commercially available synthetic leathers with respect to variousproperties. The results are shown in table 2 EXAMPLE 10 and in the samemanner as in example 8, three kinds of resin FIG. 3 is a plot ofthickness against apparent density for solution were prepared. Namely,we provided a solution havthree leathers, of which curve I is for thesynthetic leather of i a i it f 1 oi e re ared b di olving a copolymcrthe Present invention: curve is for comparison Sample A and of 35 moleacrylonitrile and 65 mole butadiene in dimethylforcurve ill is forcomparison sample B. mamide to a concentration of 10 percent, and twosolutions Sample A was obtained by the following procedure. The having aviscosity of 200 poises and 850 poises respectively punched web was dipcoated with the said solution I under the prepared by adding to the saidsolution 5 parts by weight of same conditions, immersed in water at 20C. for 30 minutes carbon black and 20 parts by weight of cellulosepowder havto coagulate the resin, and dried for 10 minutes in a hot airing an average particle size of 20 microns, all amounts being dryer at120 C. One surface of the web was then coated with based on 100 parts byweight of the said solid copolymer consolution ll by means of a reverseroll coater until the takeup of tent, and diluting the solution withdimethylformamide to a the solid content reached 54 parts by weights asagainst 100 concentration of 20 percent and 25 percent respectively.

TABLE 2 Resistance Cohesion Tensile to 10% between Thickness strengthelongation layers (mm.) (kg/em.) (kg./cm.) Density gradient Bendingcharacteristic smoothness (kg./2 cm.)

Product 01 this invention 1.50 18.5 3.50 Like natural leatherJ- Likenatural leatherfi... Good Inseparable. Sample. 1.60 16.2 2.80 SomeSomewhat rubber-like... Ordinary.... 2.2. SampleB 1.50 15.0 2.02 AbsentRubber-like Poor 2.0. Commercially available 1.50 18.5 6.2 .do ..do Good0.8.

product A. Commercially available 1.50 16.0 2.7 do. do Ordinary... 2.2.

product B.

1 See curve I in Fig. 3.

7 See curve 11 in Fig. 3.

3 See curve 111 in Fig. 3.

4 The "like natural leather" means that in a bending test of a syntheticleather at the radius of curvature of 0.5-1.0 cm., a bending resistanceBi measured when the leather is bent with the surface (grain side)directed outwardly and a bonding resistance Bi, measured when theleather is bent with the said surface directed inwardly satisfy thefollowing relation: Bt B The needle-punched web of example 8 was coatedwith the three solutions in the order of a lower viscosity to give asynthetic leather excellent in cohesion between layers and smoothnesswhich had a continuous density gradient.

EXAMPLE 1 1 One surface of the web of example 8 containing solution Iwas coated with a resin solution having a concentration of 30 percentand a viscosity of 2,000 poises obtained by adding 20 parts ofpoly(vinyl chloride), 10 parts of plasticizer (DO?) and 50 parts ofcellulose powder having an average particle size of microns, all amountsbeing based on 100 parts of the solid polyurethane content, to thepolyurethane solution used in example 8 and diluting the solution withdimethylformamide, and further with a resin solution having aconcentration of 36 percent and a viscosity of 1,300 poises prepared byadding 10 parts of a plasticizer (DOP) and 30 parts of calciumcarbonate, all amounts based on 100 parts of the solid polyu rethanecontent, to the said polyurethane solution, and diluting it withdimethylformamide. The subsequent treatment in the same manner as inexample 8 gave a synthetic leather excellent in smoothness and cohesionbetween layers having a continuous density gradient.

EXAMPLE 12 A web having a weight per unit area of 250 g/m was producedby means of a random webber from nylon 6 staples having a denier of 3, afiber length of 51 mm., a number of crimps of turns/inch, and a titaniumoxide content of 0.2 percent. The resulting web was passed through apair of hot rolls heated to 160 C., and set to a thickness of 1.0 mm.The same treatment as in example 9 of this web gave a similar syntheticleather.

We claim:

1. A process for manufacturing synthetic leather, which comprisesimpregnating a fiber web with a solution ofa binder and solvent, coatingone surface of the web prior to coagulation of the binder, with asolution of a synthetic resin and sol' vent having a viscosity higherthan that of the binder solution, and simultaneously coagulating thebinder and synthetic resin by a wet method wherein the solvents areextracted in a liquid which is compatible with the solvents.

2. The process according to claim 1, wherein the binder and syntheticresin are the same type of polymer.

3. A process for manufacturing synthetic leather, which comprisesimpregnating a fiber web with a solution ofa binder and solvent,applying to one surface of the web prior to coagulation of the saidbinder, and in the order of increasing viscosities, a plurality ofbinder solutions exhibiting viscosities differing each from the others,each binder solution having a viscosity higher than the binder solutioninitially impregnated into the web, coating this same surface of the webprior to coagulation of the binder solutions, with a solution of asynthetic resin and solvent having a viscosity higher than thelast-applied binder solution and within the range of 50-l0,000 poises,and simultaneously coagulating the binders and synthetic resin by a wetmethod wherein the solvents are extracted in a liquid which iscompatible with the solvents.

4. The process according to claim .3, wherein each of the binders andthe synthetic resin are the same type of polymer.

5. A process for manufacturing synthetic leather, which comprises a.forming a fiber web of a weight per unit area of -1 ,000 g,/cm.,

b. needle punching the web utilizing a needle penetration depth of 6-12mm.,

c. impregnating the needle punched web with a solution ofa binder andsolvent having a viscosiity of 0. 1l00 poises,

d. coating one surface of the web prior to coagulation of the binder,with a solution of a synthetic resin and solvent having a viscosityhigher than that of the binder solution and within the range of50-10,000 poises whereby liquidliquid mixing between the binder solutionand synthetic resin solution is effected at the interface of therespective solutions,

e. simultaneously coagulating the binder and synthetic resin with water,and

f. drying the resultant product.

6. A process for manufacturing synthetic leather, which comprises a.forming a fiber web of a weight per unit area of l001,000 g./cm.

. needle punching the web utilizing a needle penetration depth of 612mm.,

. impregnating the needle-punched web with a solution of a binder andsolvent having a viscosity of 0.l100 poises, applying to one surface ofthe web prior to coagulation of the said binder, and in the order ofincreasing viscosities, a plurality of binder solutions exhibitingviscosities differing each from the others, each binder solution havinga viscosity higher than the binder solution initially impregnated intothe web,

. coating this same surface of the web prior to coagulation of thebinder solutions, with a solution of a synthetic resin and solventhaving a viscosity higher than the lastapplied binder solution andwithin the range of 50l0,000 poises whereby liquid-liquid mixing amongthe binder solutions and synthetic resin solution is effected at theinterfaces of the the solutions in the order in which they were applied,

e. simultaneously coagulating the binder solutions and synthetic resinsolution with water, and

f. drying the resultant product.

2. The process according to claim 1, wherein the binder and syntheticresin are the same type of polymer.
 3. A process for manufacturingsynthetic leather, which comprises impregnating a fiber web with asolution of a binder and solvent, applying to one surface of the webprior to coagulation of the said binder, and in the order of increasingviscosities, a plurality of binder solutions exhibiting viscositiesdiffering each from the others, each binder solution having a viscosityhigher than the binder solution initially impregnated into the web,coating this same surface of the web prior to coagulation of the bindersolutions, with a solution of a synthetic resin and solvent having aviscosity higher than the last-applied binder solution and within therange of 50-10,000 poises, and simultaneously coagulating the bindersand synthetic resin by a wet method wherein the solvents are extractedin a liquid which is compatible with the solvents.
 4. The processaccording to claim 3, wherein each of the binders and the syntheticresin are the same type of polymer.
 5. A process for manufacturingsynthetic leather, which comprises a. forming a fiber web of a weightper unit area of 100-1,000 g./cm.2, b. needle punching the web utilizinga needle penetration depth of 6-12 mm., c. impregnating the needlepunched web with a solution of a binder and solvent having a viscosityof 0.1-100 poises, d. coating one surface of the web prior tocoagulation of the binder, with a solution of a synthetic resin andsolvent having a viscosity higher than that of the binder solution andwithin the range of 50-10,000 poises whereby liquid-liquid mixingbetween the binder solution and synthetic resin solution is effected atthe interface of the respective solutions, e. simultaneously coagulatingthe binder and synthetic resin with water, and f. drying the resultantproduct.
 6. A process for manufacturing synthetic leather, whichcomprises a. forming a fiber web of a weight per unit area of 100-1,000g./cm.2, b. needle punching the web utilizing a needle penetration depthof 6-12 mm., c. impregnating the needle-punched web with a solution of abinder and solvent having a viscosity of 0.1-100 poises, applying to onesurface of the web prior to coagulation of the said binder, and in theorder of increasing viscosities, a plurality of binder solutionsexhibiting viscosities differing each from the others, each bindersolution having a viscosity higher than the binder solution initiallyimpregnated into the web, d. coating this same surface of the web priorto coagulation of the binder solutions, with a solution of a syntheticresin and solvent having a viscosity higher than the last-applied bindersolution and within the range of 50-10,000 poises whereby liquid-liquidmixing among the binder solutions and synthetic resin solution iseffected at the interfaces of the the solutions in the order in whichthey were applied, e. simultaneously coagulating the binder solutionsand synthetic resin solution with water, and f. drying the resultantproduct.